I've read reports that the global bee population is not actually decreacing. The poplution seem to be decreasing in the USA and a few other areas in Great Britaitn and Holand, but overall there's no evidence of the world population being signifficantly lowered.

This is the only source I could find with a quick search, and it's in spanish [PDF]http://www.fcen.uba.ar/prensa/cable/2010/pdf/Cable_752.pdf